Assuming he didn’t bug the FBI director at dinner, when could he have done it legally?
It turns out it would be legal in Washington DC for him to record the phone conversation:
http://www.dmlp.org/legal-guide/district-columbia-recording-law

The District of Columbia’s wiretapping law is a “one-party consent” law. DC makes it a crime to record a phone call or conversation unless one party to the conversation consents. See D.C. Code § 23-542. Thus, if you operate in DC, you may record a conversation or phone call if you are a party to the conversation or you get permission from one party to the conversation in advance. That said, if you intend to record conversations involving people located in more than one state, you should play it safe and get the consent of all parties.

However in Florida it isn’t, and we all know how much time Trump spends there ‘working’:
http://www.dmlp.org/legal-guide/florida-recording-law

Florida’s wiretapping law is a “two-party consent” law. Florida makes it a crime to intercept or record a “wire, oral, or electronic communication” in Florida, unless all parties to the communication consent. See Fla. Stat. ch. 934.03. Florida law makes an exception for in-person communications when the parties do not have a reasonable expectation of privacy in the conversation, such as when they are engaged in conversation in a public place where they might reasonably be overheard. If you are operating in Florida, you may record these kinds of in-person conversations without breaking the law. However, you should always get the consent of all parties before recording any telephone conversation and any in-person that common sense tells you is private.

In addition to subjecting you to criminal prosecution, violating the Florida wiretapping law can expose you to a civil lawsuit for damages by an injured party.

Federal law is ‘One party consent’ just like DC

That said, I don’t think Comey ever gave Trump those assurances, or that Trump recorded him.

The people who voted for Trump are asses.
But I’m sure there are Democratic and Liberal voters who are asses, too.

But the people in his party who still make excuses for Trump, who cover up for him and look
the other way, even when they privately despise his excesses and outrages, are not asses.
They are amoral cynics and opportunists. I have no use for them.

We may yet have something to thank Donald Trump for. He has helped us see who these people are, has allowed us to expose them for the corrupt hypocrites they are. Thank you, Donald, and thank you, Trump voter. You can’t help the way you are.
But TB and SDAI, you CAN help it. You know better.

Remember, some of you voted for this… and you will NEVER be allowed to forget that.

Assuming we all get out of this alive, you have to know how this will be taught to your grandchildren and great grand-children, don’t you? Those of you that supported this man will be remembered as the gullible, moronic, bigoted villains of this period of history- the fools that believed that a wealthy reality TV star would make the lives of the ‘little people’ better, that a misogynist bigot was the best face to represent our nation. You will be remembered as the people willing to overlook treason because you wanted the ‘freedom’ to insult and injure minorities.

Look on the bright side- maybe your stupidity will lead to a LITERAL ‘DEFCON ONE’- in which case you won’t have to live with your mistakes very long… that really is your best-case scenario at this point.

They simply believe that they should be able to do whatever they want and not be held accountable to anyone – not the American public, not even the law.